Preheat oven to 170°C/340°F.Mix together the matzo flour, sugar and vanilla sugar. Set aside.Melt the chocolate and butter together over low heat until smooth.Mix the melted chocolate into the flour mixture. Add the eggs, brandy, walnuts and chocolate chips, if using, and stir to incorporate.Pour into a greased 20x30-cm. baking pan and bake for about 25 minutes, until a toothpick inserted in the center comes out dry.